1. Field of the Invention
Methods consistent with the present invention relate to coding motion picture frames, and more particularly, to encoding and decoding motion picture frames while reducing flickering caused by unnatural picture conversion, when Instantaneous Decoding Refresh-I (IDR-I) frames are reproduced.
2. Description of the Related Art
The latest video coding standard, H.264, enhances encoding efficiency and performance using a variety of new techniques. Specifically, the H.264 standard defines an Instantaneous Decoding Refresh (IDR) frame in order to provide random access and prevent error propagation. The H.264 standard uses a plurality of reference frames that can be located far away from a current frame in a display order. The reference frames are restored in advance in a decoding order, stored in a memory space called a Decoded Picture Buffer (DPB), managed in the same way by an encoder and a decoder, and used for picture encoding and decoding. In order to allow the decoder to randomly access an encoded bit stream, encoding is performed using an IDR-I frame at a predetermined interval. When encoding is performed using an IDR-I frame, the encoder resets and empties all reference frames previously restored and stored in the DPB, and encodes pictures following the IDR-I frame with reference to only frames following the IDR-I frame. Accordingly, since the frames following the IDR-I frame have no correlation with the preceding frames, random access is allowed from the location of the IDR-I frame.
However, in the case of encoding using IDR-I frames to allow random access, the encoding efficiency of pictures adjacent to each IDR-I frame deteriorates compared to encoding using I frames, and picture flickering occurs due to low consistency of pictures. Although an I frame and an IDR-I frame maintain the same picture quality, differences in picture quality will exist between pictures following the I frame and pictures following the IDR-I frame. When encoding is performed using I frames, P and B frames following each I frame can refer to P frames before the I frame appears. However, when encoding is performed using IDR-I frames, P and B frames following each IDR-I frame cannot refer to any frame before the IDR-I frame appears. Accordingly, picture consistency deteriorates from the location of the IDR-I frame, so that unnatural picture conversion, for example, screen flickering, etc., appears.